The present invention generally relates to a free radical polymerization process and particularly relates to a free radical polymerization process utilizing chain transfer agents (CTAs) and to polymers made therefrom.
There is increasing interest in developing polymerization processes that can be predictably controlled to produce polymers having specifically desired structures. One of the means for achieving such results is through a process of living polymerization. Such a process provides a higher degree of control during the synthesis of polymers having predictably well defined structures and properties as compared to polymers made by conventional polymerization processes.
Certain xanthate and dithiocarbamate derivatives of the following formula 1: 
where Q=O(alkyl) or N(alkyl)2, respectively have been shown to confer some of the characteristics of living polymerization when used as photoinitiators in polymerization processes (see for example Otsu et al., U.S. Pat. No. 5,314,962). Such a process where radicals are generated by direct photolysis of the xanthate or dithiocarbamate derivative do not form part of this invention. See also Niwa et al. (Makromol. Chem., 189, 2187 (1988)) and Otsu et al. (Macromolecules 19, 287 (1986)).
Free radical polymerizations in the presence of chain transfer agents (CTAs) represented by formula 1 (where Q=Zxe2x80x2 and R are as defined herein) have been disclosed by Le et al. in Int. Patent Application WO 98/01478, which discloses, that since dithiocarbamate and xanthate derivatives disclosed therein have very low transfer constants they are therefore ineffective in conferring living characteristics on a free radical polymerization. However, we have surprisingly found that by appropriate selection of substituents (Q) or the monomer these agents have high chain transfer constants and are effective in conferring living characteristics to a free radical polymerization. The CTAs of the present invention can also advantageously introduce novel end group functionalities into the resulting polymers.
The present invention is directed to a process for producing a polymer, said process comprising polymerizing a monomer mix into said polymer in the presence of a source of free radicals and a chain transfer agent having a transfer constant in the range of from 0.1 to 5000, said chain transfer agent having the following formula: 
wherein when D is D1 of the following formula: 
then p is in the range of from 1 to 200, E is Zxe2x80x2 and said transfer agent is of the following formula: 
wherein when D is D2 of the following formula: 
then p is in the range of from 1 to 200, E is E1 or E2 and said transfer agent is of the following formula: 
wherein when D is D3 of the following formula: 
then pxe2x80x2 is in the range of from 2 to 200, E is Z, E1 or E2 and said transfer agent is of the following formula: 
wherein when D is D4 of the following formula:
xe2x80x94Sxe2x80x94Rxe2x80x2
then E is E3 or E4 and said transfer agent is of the following formula: 
where in an of the above:
R is a p-valent moiety derived from a moiety selected from the group consisting of substituted or unsubstituted alkane, substituted or unsubstituted alkene, substituted or unsubstituted arene, unsaturated or aromatic carbocyclic ring, unsaturated or saturated heterocyclic ring, an organometallic species, and a polymer chain, Rxe2x80xa2 being a free radical leaving group resulting from R that initiates free radical polymerization;
R* and Rxe2x80x2 are monovalent moieties independently selected from the group consisting of a substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted aryl, unsaturated or aromatic carbocyclic ring, unsaturated or saturated heterocyclic ring, substituted or unsubstituted alkylthio, substituted or unsubstituted alkoxy, substituted or unsubstituted dialkylamino, an organometallic species, and a polymer chain, R*xe2x80xa2 being a free radical leaving group resulting from R* that initiates free radical polymerization;
X is selected from the group consisting of a substituted or unsubstituted methine, nitrogen, and a conjugating group;
Zxe2x80x2 is selected from the group consisting of E1, E2, halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted aryl, substituted or unsubstituted heterocyclyl, substituted or unsubstituted alkylthio, substituted or unsubstituted alkoxycarbonyl, substituted or unsubstituted xe2x80x94COORxe2x80x3, carboxy, substituted or unsubstituted xe2x80x94CONRxe2x80x32, cyano, xe2x80x94P(xe2x95x90O)(ORxe2x80x3)2, xe2x80x94P(xe2x95x90O)Rxe2x80x32;
Rxe2x80x3 is selected from the group consisting of substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted aryl, substituted or unsubstituted heterocyclyl, substituted or unsubstituted aralkyl, substituted or unsubstituted alkaryl, and a combination thereof;
Zxe2x80x3 is a pxe2x80x2-valent moiety derived from a moiety selected from the group consisting of a substituted or unsubstituted alkane, substituted or unsubstituted alkene, substituted or unsubstituted arene, substituted or unsubstituted heterocycle, a polymer chain, an organometallic species, and a combination thereof;
Z is selected from the group consisting of a halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted aryl substituted or unsubstituted heterocyclyl, substituted or unsubstituted alkylthio, substituted or unsubstituted alkoxycarbonyl, substituted or unsubstituted xe2x80x94COORxe2x80x3, carboxy, substituted or unsubstituted xe2x80x94CONRxe2x80x32, cyano, xe2x80x94P(xe2x95x90O)(ORxe2x80x3)2, xe2x80x94P(xe2x95x90O)Rxe2x80x32;
E1 is a substituent functionality derived from a substituted or unsubstituted heterocycle attached via a nitrogen atom, or is of the following formula: 
wherein G and J are independently selected from the group consisting of hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkoxy, substituted or unsubstituted acyl, substituted or unsubstituted aroyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkylsulfonyl, substituted or unsubstituted alkylsulfinyl, substituted or unsubstituted alkylphosphonyl, substituted or unsubstituted arylsulfonyl, substituted or unsubstituted arylsulfinyl, substituted or unsubstituted arylphosphonyl;
E2 is of the following formula: 
wherein Gxe2x80x2 is selected from the group consisting of substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted aryl;
E3 is of the following formula 
wherein pxe2x80x2xe2x80x3 is between 2 and 200, Gxe2x80x3 is Zxe2x80x3 and Jxe2x80x2 is independently selected from the group consisting of hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkoxy, substituted or unsubstituted acyl, substituted or unsubstituted aroyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkylsulfonyl, substituted or unsubstituted alkylsulfinyl, substituted or unsubstituted alkylphosphonyl, substituted or unsubstituted arylsulfonyl, substituted or unsubstituted arylsulfinyl, substituted or unsubstituted arylphosphonyl or is joined to Gxe2x80x3 so as to form a 5-8 membered ring; and
E4 is of the following formula 
wherein pxe2x80x2xe2x80x3 is between 2 and 200 and Gxe2x80x2xe2x80x3 is Zxe2x80x3.
The present invention is also directed to polymers made by the process of the current invention. One of the embodiment is the polymer is of the following formula: 
where n is a positive integer in the range of from 1 to 100,000 and wherein A is of the following formula: 
when D is D1 and E is Zxe2x80x2;
A is of the following formula: 
when D is D2 and E is E1; or
A is of the following formula: 
when D is D2 and E is E2; and
and Qxe2x80x3 is a repeat unit derived from a monomer selected from the group consisting of maleic anhydride, N-alkymaleimide, N-arylmaleimide, dialkyl fumarate, cyclopolymerizable monomer, a ring opening monomer, a macromonomer, a vinyl monomer of the following formula: 
and a combination thereof;
wherein L is selected from the group consisting of hydrogen, halogen, and substituted or unsubstituted C1-C4 alkyl, said alkyl substituents being independently selected from the group consisting of hydroxy, alkoxy, ORxe2x80x3, CO2H, O2CRxe2x80x3, CO2Rxe2x80x3 and a combination thereof; and
wherein M is selected from the group consisting of hydrogen, Rxe2x80x3, CO2H, CO2Rxe2x80x3, CORxe2x80x3, CN, CONH2, CONHRxe2x80x3, CONRxe2x80x32, O2CRxe2x80x3, ORxe2x80x3, and halogen.
Another embodiment is the polymer comprising a mixture of isomers of the following formula: 
where n is a positive integer in the range of from 1 to 100,000, D is D3, E is Z, E1 or E2.
Still another embodiment is the polymer is of the following formula: 
where n is a positive integer in the range of from 1 to 100,000, D is D4, and E is E3.
A further embodiment is the polymer is of the following formulae: 
where n is a positive integer in the range of from 1 to 100,000, D is D4, and E is E4.
One of the advantages of the present polymerization system is that by controlling the reaction stoichiometry and the degree of conversion of the monomers into polymer the process produces polymers of predetermined molecular weight and narrow molecular weight distnbution over a wide range of monomers and reaction conditions.
Another advantage of the process of the present invention is that by successively adding different monomers to the reaction mixture, block polymers of low polydispersity and desired molecular weight can be produced.
Still another advantage of the process of the present invention is that it is possible to create polymers having complex structures, such as graft, star and branched polymers.
Yet another advantage of the present invention is that it is suitable for carrying out emulsion, solution, or suspension polymerization in either a batch, semi-batch, continuous or feed mode.
Still another advantage of the present invention is that it is suitable for producing waterborne polymers that are water soluble or water dispersible.
Another advantage of the present invention is that it is suitable for producing solvent borne polymers that are solvent soluble or solvent dispersible.
As defined herein:
xe2x80x9cLiving polymerizationxe2x80x9d means a process which proceeds by a mechanism whereby most chains continue to grow throughout the polymerization and where further addition of monomer results in continued polymerization (block copolymers can be prepared by sequential monomer addition of different monomers). The molecular weight is controlled by the stoichiometry of the reaction and narrow molecular weight distribution polymers can be produced.
xe2x80x9cRadical leaving groupxe2x80x9d means a group attached by a bond capable of undergoing homolytic scission during a reaction to thereby form a free radical.
xe2x80x9cGPC number average molecular weightxe2x80x9d (Mn) means a number average molecular weight and xe2x80x9cGPC weight average molecular weightxe2x80x9d (Mw) means a weight average molecular weight measured by utilizing gel permeation chromatography. A Waters Associates liquid chromatograph equipped with differential refractometer and 106, 105, 104, 103, 500 and 100 xc3x85 Ultrastyragel columns was used. Tetrahydrofuran (flow rate of 1.0 mL/min) was used as an eluent. The molecular weights were provided as polystyrene equivalents.
xe2x80x9cPolydispersityxe2x80x9d (Mw/Mn) means GPC weight average molecular weight divided by GPC number average molecular weight.
xe2x80x9cAddition-fragmentationxe2x80x9d is a two-step chain transfer mechanism wherein a radical addition is followed by fragmentation to generate new radical species.
xe2x80x9cChain transfer constantxe2x80x9d means the ratio of the rate constant for chain transfer to the rate constant for propagation at zero conversion of monomer and CTA. If chain transfer occurs by addition-fragmentation, the rate constant for chain transfer (ktr) is defined as follows:       k    tr    =            k      add        xc3x97                  k        β                              k                      -            add                          +                  k          β                    
where kadd is the rate constant for addition to the CTA and kxe2x88x92add and kxcex2 are the rate constants for fragmentation in the reverse and forward directions respectively.
xe2x80x9cPolymer chainxe2x80x9d means conventional condensation polymers, such as polyesters [for example, polycaprolactone, poly(ethylene terephthalate)], polycarbonates, poly(alkylene oxide)s [for example, poly(ethylene oxide), poly(tetramethylene oxide)], nylons, polyurethanes or addition polymers such as those formed by coordination polymerization (for example polyethylene, polypropylene), radical polymerization (for example poly(meth)acylates and polystyrenics or anionic polymerization (for example polystyrene, polybutadiene).
xe2x80x9cCyclopolymerizable monomersxe2x80x9d means compounds which contain two or more unsaturated linkages suitably disposed to allow propagation by a sequence of intramolecular and intermolecular addition steps leading the incorporation of cyclic units into the polymer backbone. Most compounds of this class are 1,6-dienes such asxe2x80x94diallylammonium salts (e.g., diallyldimethylammonium chloride), substituted 1,6-heptadienes (e.g., 6-dicyano-1,6-heptadiene, 2,4,4,6-tetrakis(ethoxycarbonyl)-1,6-heptadiene) and monomers of the following generic structure 
where substituents K, Kxe2x80x2, T, B, Bxe2x80x2 are chosen such that the monomer undergoes cyclopolymerization. For example:
B, Bxe2x80x2 are indepdently selected from the group consisting of H, CH3, CN, CO2Alkyl, Ph; K, Kxe2x80x2 are selected from the group consisting of CH2, Cxe2x95x90O, Si(CH3)2, O; T is selected from the group consisting of C(E)2, O, N(Alkyl)2 salts, P(Alkyl)2 salts, P(O)Alkyl. Additional monomers listed in Moad and Solomon xe2x80x9cThe Chemistry of Free Radical Polymerizationxe2x80x9d, Pergamon, London, 1995, pp 162-170, are also suitable.
xe2x80x9cRing opening monomnersxe2x80x9d are monomers which contain a suitably disposed carbocyclic or heterocyclic ring to allow propagation by a sequence of intermolecular addition and intramolecular ring opening steps such as those described in Moad and Solomon xe2x80x9cThe Chemistry of Free Radical Polymerizationxe2x80x9d, Pergamon, London, 1995,pp 171-186.
xe2x80x9cOrganometallic speciesxe2x80x9d means a moiety containing one or more metal atoms from Groups III and IV of the Periodic Table and transition elements and organic ligands, preferably species, such as, Si(X)3, Ge(X)3 and Sn(X)3 which provide radical leaving groups and initiate polymerization, X being a group discussed later in the specification.
xe2x80x9cHeterocyclicxe2x80x9d or xe2x80x9cheterocyclylxe2x80x9d means a ring structure containing 3 to 18 atoms at least one of which is selected from O, N and S, which may or may not be aromatic. Examples of xe2x80x9cheterocyclylxe2x80x9d moieties are pyridyl furanyl, thienyl, piperidinyl, pyrrolidinyl, pyrazoyl, benzthiazolyl, indolyl, benzofuranyl, benzothiophenyl, pyrazinyl, and quinolyl, optionally substituted with one or more of alkyl, haloalkyl and halo groups.
xe2x80x9cSubstituent functionality derived from a substituted or unsubstituted heterocycle attached via a nitrogen atomxe2x80x9d means the group formed by excising monovalent nitrogen (e.g.  greater than NH) from an appropriate nitrogen containing heterocycle. Said heterocycles include pyrrolidine, pyrrole, indole, imidazole, carbazole, benzimidazole, benzotriazole, piperidine and isatin, all of which may be substituted or unsubstituted. For example, in the case of pyrrole, the substituent functionality is 1,3-butadiene-1,4-diyl, and in the case of pyrrolidine it is butane-1,4-diyl.
Unless specified otherwise, alkyl groups referred to in this specification may be branched or unbranched and contain from 1 to 18 carbon atoms. Alkenyl groups may be branched or unbranched and contain from 2 to 18 carbon atoms. Saturated or unsaturated or carbocyclic or heterocyclic rings may contain from 3 to 18 atoms. Aromatic carbocyclic or heterocyclic rings may contain 5 to 18 carbon atoms.
xe2x80x9cConjugating groupxe2x80x9d is one which provides orbital overlap between the Cxe2x95x90S double bond and the lone pair of the Sxe2x80x94R group, in the case of compounds of formula 2 described below, where D=D1, or to the nitrogen lone pair in the case of conmpounds of the formula 2, where D=D2, E=E1 thereby providing for delocalization of the associated electrons. Examples of such conjugating groups are provided in the subsequent text.
xe2x80x9cSubstitutedxe2x80x9d means that a group may be substituted with one or moe groups that are independently selected from the group that consisting of alkyl, aryl, epoxy, hydroxy, alkoxy, oxo, acyl, acyloxy, carboxy, carboxylate, sulfonic acid, sulfonate, alkoxy- or aryloxy-carbonyl, isocyanato, cyano, silyl, halo, dialkylamino, and amido. All substituents are chosen such that there is no substantial adverse interaction under the conditions of the experiment.
We have discovered a novel free radical polymerization process and novel polymers produced therefrom. The process is direcd to polymerizing a monomer mix in the presence of a source of free radicals and at least one of certain sulfur based CTAs chosen so as to confer living characteristics. By utilizing these CTAs, polymers of controlled molecular weight and low polydispersity can be obtained.
The sulfur based CTAs suitable for use in the present invention have a chain transfer constants in the range of from 0.1 to 5000, preferably in the range of from 1 to 2000 and more preferably in the range of from 10 to 500. If the chain transfer constant of the CTA exceeds the upper limit of the range substantially no polymerization occurs, if it falls below the lower limit it is not possible to prodce polymers having low polydispersity. The CTAs of the present invention generally should not copolymerize with monomers during the polymerization process. As a result, low polydispersity polymers based on monosubstituted monomers (e.g., acrylic monomers, styrene) can be made under a wide range of reaction conditions.
The sulfur based CTA suitable for use in the present process is of the formula 2 below: 
wherein when D is D1 of the following formula 3 below: 
then p is in the range of from 1 to 200, E is Zxe2x80x2 and said transfer agent is of the following formula 4 below: 
wherein when D is D2 of the following formula 5 below: 
then p is in the range of from 1 to 200, E is E1 or E2 and said transfer agent is of the following formula 6 below: 
wherein when D is D3 of the following formula 7 below: 
then pxe2x80x2 is in the range of from 2 to 200, E is Z, E1 or E2 and said transfer agent is of the following formula 8 below: 
wherein when D is D4 of the following formula 9 below:
xe2x80x94Sxe2x80x94Rxe2x80x2xe2x80x83xe2x80x83(9)
then E is E3 or E4 and said transfer agent is of the following formula 10: 
where in all of the above:
R is a p-valent moiety derived from a moiety selected from the group consisting of a substituted or unsubstituted alkane, substituted or unsubstituted alkene, substituted or unsubstituted arene, unsaturated or aromatic carbocyclic ring, unsaturated or saturated heerocyclic ring, an organometallic species, and a polymer chain, Rxe2x80xa2 being a free radical leaving group resulting from R that initiates free radical polymerization;
R* and Rxe2x80x2 are monovalent moieties independently selected from the group consisting of a substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted aryl, unsaturated or aromatic carbocyclic ring, unsaturated or saturated heterocyclic ring, substituted or unsubstituted alkylthio, substituted or unsubstituted alkoxy, substituted or unsubstituted dialkylamino, an organometallic species, and a polymer chain, R*xe2x80xa2 being a free radical leaving group resulting from R* that initiates free radical polymerization;
X is selected from the group consisting of a substituted or unsubstituted methine, nitrogen, and a conjugating group;
Zxe2x80x2 is selected from the group consisting of E1, E2, halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted aryl, substituted or unsubstituted heterocyclyl, substituted or unsubstituted alkylthio, substituted or unsubstituted alkoxycarbonyl, substituted or unsubstituted xe2x80x94COORxe2x80x3, carboxy, substituted or unsubstituted xe2x80x94CONRxe2x80x32, cyano, xe2x80x94P(xe2x95x90O)(ORxe2x80x3)2, xe2x80x94P(xe2x95x90O)Rxe2x80x32;
Rxe2x80x3 is selected from the group consisting of substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted aryl, substituted or unsubstituted heterocyclyl, substituted or unsubstituted aralkyl, substituted or unsubstituted alkaryl, and a combination thereof;
Zxe2x80x3 is a pxe2x80x2-valent moiety derived from a moiety selected from the group consisting of a substituted or unsubstituted alkane, substituted or unsubstituted alkene, substituted or unsubstituted arene, substituted or unsubstituted heterocycle, a polymer chain, an organometallic species, and a combination thereof;
Z is selected from the group consisting of a halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted aryl, substituted or unsubstituted heterocyclyl, substituted or unsubstituted alkylthio, substituted or unsubstituted alkoxycarbonyl, substituted or unsubstituted xe2x80x94COORxe2x80x3, carboxy, substituted or unsubstituted xe2x80x94CONRxe2x80x32, cyano, xe2x80x94P(xe2x95x90O)(ORxe2x80x3)2, xe2x80x94P(xe2x95x90O)Rxe2x80x32;
E1 is a substituent functionality derived from a substituted or unsubstituted heterocycle attached via a nitrogen atom, or is of the following formula 11: 
wherein G and J are independently selected from the group consisting of hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkoxy, substituted or unsubstituted acyl, substituted or unsubstituted aroyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkylsulfonyl, substituted or unsubstituted alkylsulfinyl, substituted or unsubstituted alkylphosphonyl, substituted or unsubstituted arylsulfonyl, substituted or unsubstituted arylsulfinyl, substituted or unsubstituted arylphosphonyl; and
E2 is of the following formula 12: 
wherein Gxe2x80x2 is selected from the group consisting of substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted aryl;
E3 is of the following formula 13: 
wherein pxe2x80x2xe2x80x3 is between 2 and 200, Gxe2x80x3 is Zxe2x80x3 and Jxe2x80x2 is independently selected from the group consisting of hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkoxy, substituted or unsubstituted acyl, substituted or unsubstituted aroyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkylsulfonyl, substituted or unsubstituted alkylsulfinyl, substituted or unsubstituted alklphosphonyl, substituted or unsubstituted arylsulfonyl, substituted or unsubstituted arylsulfinyl, substituted or unsubstituted arylphosphonyl; and
E4 is of the following formula 14: 
wherein pxe2x80x2xe2x80x3 is between 2 and 200 and Gxe2x80x2xe2x80x3 is Zxe2x80x3.
The foregoing CTAs are prepared by the following processes:
Vinylogous dithioesters may be prepared in several ways. For example, 3-benzylthio-5,5-dimethylcyclohex-2-ene-1-thione is made by a multi-step process. First, piperidine is condensed with 5,5-dimethylcyclohexane-1,3-dione in the presence of a strong acid to form enaminoketone, which is then converted to a thione derivative. After the addition of benzyl chloride and hydrogen sulfide work-up, the 3-benzylthio-5,5-dimethylcyclohex-2-ene-1-thione is isolated as a purple oil.
The preparation of benzyl 3,3-di(benzylthio)prop-2-enedithioate, another vinylogous dithioester, starts with addition of two moles of carbon disulfide to one mole of the Grignard reagent, such as, methyl magnesium chloride. Treatment with strong base at low temperature followed by addition of benzyl chloride results in the dithioate, which is an orange solid.
The thiocarbonylthio compounds with alpha-nitrogen atoms are synthesized from the corresponding nitrogen compounds. For example, benzyl 1-pyrrolecarbodithioate is prepared by adding pyrrole to sodium hydride suspension in dimethyl sulfoxide followed by the addition of carbon disulfide. Benzyl chloride is added and the product, benzyl 1-pyrrolecarbodithioate, is isolated by extraction with diethyl ether.
The corresponding 2-pyrrolidineone derivative is prepared in a similar manner by starting with pyrrolidone instead of pyrrole.
Benzyl (1,2-benzenedicarboximido)carbodithioate is prepared by carbon disulfide addition to potassium phthalimide. Benzyl chloride is then added to complete the synthesis.
Bis(thiocarbonyl) disulfides masy be the starting material for other dithioate compounds. 2,2xe2x80x2-azobis(2cyanopropane) is thermally decomposed in the presence of pyrrole N-thiocarbonyl disulfide to produce 2-cyanoprop-2-yl 1-pyrrolecarbodithioate. 2-Cyanobut-2-yl 1-pyrrolecarbodithioate is prepared by the same method using 2,2xe2x80x2-azobis(2-cyanobutane) and pyrrole N-thiocarbonyl disulfide.
Benzyl 1-imidazolecarbodithioate may be prepared by yet another method. Benzyl mercaptan is added to a solution of thiocarbonyldiimidazole in dichloromethane. The compound is then isolated as a yellow oil.
The Xanthate derivatives may be prepared by adding the corresponding halocompound to potassium O-ethyl dithiocarbonate. Therefore, O-ethyl S-(1-phenylethyl)xanthate is made by adding 1-(bromoethyl)benzene to potassium O-ethyl dithiocarbonate. O-Ethyl S-(2-ethoxycarbonylprop-2-yl)xanthate is made by adding 2-bromoisobutyrate to potassium O-ethyl dithiocarbonate, and O-ethyl S-(2-cyanoisopropyl)xanthate is made by adding 2-bromoisobutyronitrile to potassium O-ethyl dithiocarbonate.
Some of the preferred CTAs include the following:
1. The CTA which includes D1 of the formula 15 below: 
when E1 is of the formula 16 below: 
2. The CTA which includes D2 of the formula 17 below: 
when E1 is of the formulas 18-20 below: 
or E2 is of the formulas 21 or 22 below: 
3. The CTA which includes D2 of the formulas 23 or 24 below: 
when E1 is of the formula 25 below: 
4. The CTA which includes D2 of the formulas 26, 27 or 28 below: 
when E2 is of the formula 29 below:
xe2x80x94Oxe2x80x94C2H5xe2x80x83xe2x80x83(29)
If desired, the CTA of the formula 2 further includes acyclic structure when D is D1 and Zxe2x80x2 and E are such that Exe2x80x94Cxe2x80x94Xxe2x95x90Cxe2x80x94Zxe2x80x2 forms a ring structure. The bridging functionality forms a bridge between Zxe2x80x2 and E. When such as a cyclic structure is present, Zxe2x80x2 and E may not be halogen, methyl or carboxy functionality.
One of the CTAs having the bridging functionality is of the following formula 30 below where E, Zxe2x80x2=neopentylene: 
The source of free radicals suitable for use in the present invention includes those compounds that provide free radicals that add to monomers to produce propagating radicals. Propagating radicals are radical species that have added one or more monomer units and are capable of adding further monomer units.
The amount of the free radical initiator used depends upon the desired polydispersity, molecular weight and polymer structure of the resulting polymer. However, generally less than 10 percent, preferably in the range of from 0.001 to 5 percent of the free radical initiator is used, all percentages being in weight percent based on the total amount of monomer mixture.
The source of initiating radicals may be any suitable method of generating free radicals that provide free radicals that add to monomers to produce propagating radicals. This includes such sources as the thermally induced homolytic scission of a suitable compound(s) (such as peroxides, peroxyesters, or azo compounds), the spontaneous generation from monomer (e.g. styrene), redox initiating systems, photochemical initiating systems or high energy radiation such as electron beam, X- or xcex3-radiation. The initiating system is chosen such that under the reaction conditions there is no substantial adverse interaction of the initiator or the initiating radicals with the transfer agent under the conditions of the experiment. The initiator should also have the requisite solubility in the reaction medium or monomer mixture.
Examples of suitable sources of free radicals for the process include azo compounds and peroxides such as:
2,2xe2x80x2-azobis(isobutyronitrile), 2,2xe2x80x2-azobis(2-cyano-2-butane), dimethyl 2,2xe2x80x2-azobis(methyl isobutyrate), 4,4xe2x80x2-azobis(4-cyanopentanoic acid), 4,4xe2x80x2-azobis(4-cyanopentan-1-ol), 1,1xe2x80x2-azobis(cyclohexanecarbonitrile), 2-(t-butylazo)-2-cyanopropane, 2,2xe2x80x2-azobis[2-methyl-N-(1,1)-bis(hydoxymethyl)-2-hydroxyethyl]propionamide, 2,2xe2x80x2-azobis[2-methyl-N-hydroxyethyl)]-propionamide, 2,2xe2x80x2-azobis(N,Nxe2x80x2-dimethyleneisobutyramidine)dihydrochloride, 2,2xe2x80x2-azobis(2-amidinopropane)dihydrochloride, 2,2xe2x80x2-azobis(N,Nxe2x80x2-dimethyleneisobutyramine), 2,2xe2x80x2-azobis(2-methyl-N-[1,1-bis(hydroxymethyl)2-hydroxyethyl]propionamide), 2,2xe2x80x2-azobis(2-methyl-N-[1,1-bis(hydroxymethyl)ethyl] propionamide), 2,2xe2x80x2-azobis[2-methy-N(2-hydroxyethyl)propionamide], 2,2xe2x80x2-azobis(isobutyramide) dihydrate, 2,2xe2x80x2-azobis(2,2,4-trimethylpentane), 2,2xe2x80x2-azobis(2-methylpropane), t-butyl peroxyacetate, t-butyl peroxybenzoate, t-butyl peroxyoctoate, t-butyl peroxyneodecanoate, t-butylperoxy isobutyrate, t-amyl peroxypivalate, t-butyl peroxypivalate, di-isopropyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, dicumyl peroxide, dibenzoyl peroxide, dilauroyl peroxide, potassium peroxydisulfate, ammonium peroxydisulfate, di-t-butyl hyponitrite, or dicumyl hyponitrite.
Free radicals may also be generated thermally from the monomer (e.g. styrene), by photochemistry, from redox initiation systems or by a combination of these methods.
Photochemical initiator systems are chosen to have the requisite solubility in the reaction medium or monomer mixture and have an appropriate quantum yield for radical production under the conditions of the polymerization. Examples include benzoin derivatives, benzophenone, acyl phosphine oxides, and photo-redox systems. Such processes where free radicals are derived by direct photolysis of the compound of formula 2 where D=D2 and E=E1 or E2 are not part of this invention.
Redox initiator systems are chosen to have the requisite solubility in the reaction medium or monomer mixture and have an appropriate rate of radical production under the conditions of the polymerization; these initiating systems may include combinations of the following oxidants and reductants:
oxidants: potassium peroxydisulfate, hydrogen peroxide, t-butyl hydroperoxide.
reductants: iron (II), titanium (III), potassium thiosulfite, potassium bisulfite.
Other suitable initiating systems are described in recent texts. See, for example, Moad and Solomon xe2x80x9cThe Chemistry of Free Radical Polymerizationxe2x80x9d, Pergamon, London, 1995, pp 53-95.
A monomer mix suitable for use in the present invention may include at least one vinyl monomer of the formula 31 below: 
where L is selected from the group consisting of hydrogen, halogen, and substituted or unsubstituted C1-C4 alkyl, said alkyl substituents being independently selected from the group consisting of OH, ORxe2x80x3, CO2H, O2CRxe2x80x3, CO2Rxe2x80x3 and a combination thereof;
where M in the formula 31 is selected from the group consisting of hydrogen, Rxe2x80x3, CO2H, CO2Rxe2x80x3, CORxe2x80x3, CN, CONH2, CONHRxe2x80x3, CONRxe2x80x32, O2CRxe2x80x3, ORxe2x80x3, and halogen.
Rxe2x80x3 is as defined above.
Depending upon the type of polymer desired, the monomer mix may also include the following monomers:
Maleic anhydride, N-alkylmaleimide, N-arylmaleimide, dialkyl fumarate, cyclopolymerizable or a ring opening monomer, or a combination thereof. The monomer mix may also include macromonomers, which are compounds of the formula 31 where L or M is a polymer chain.
The monomers or comonomers of the formula 31 generally include one or more of acrylate and methacrylate esters, acrylic and methacrylic acids, styrene, acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, vinyl esters and mixtures of these monomers, and mixtures of these monomers with other monomers. As one skilled in the art would recognize, the choice of comonomers is determined by their steric and electronic properties. The factors which determine copolymerizability of various monomers are well documented in the art. For example, see: Greenley, R. Z. in Polymer Handbook 3rd Edition (Brandup, J., and Immergut, E. H Eds.) Wiley: N.Y., 1989 p II/53.
The specific monomers or comonomers of the formula 31 include one or more of the following:
methyl methacrylate, ethyl methacrylate, propyl methacrylate (all isomers), butyl methacrylate (all isomers), 2-ethylhexyl methacrylate, isobornyl methacrylate, methacrylic acid, benzyl methacrylate, phenyl methacrylate, methacrylonitrile, alpha-methylstyrene, methyl acrylate, ethyl acrylate, propyl acrylate (all isomers), butyl acrylate (all isomers), 2-ethylhexyl acrylate, isobornyl acrylate, acrylic acid, benzyl acrylate, phenyl acrylate, acrylonitrile, styrene, functional methacrylates, acrylates and styrenes selected from glycidyl methacrylate, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate (all isomers), hydroxybutyl methacrylate (all isomers), methyl xcex1-hydroxymethyacrylate, ethyl xcex1-hydroxymethyacrylate, butyl xcex1-hydroxymethyacrylate, N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl methacrylate, triethyleneglycol methacrylate, itaconic anhydride, itaconic acid, glycidyl acrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate (all isomers), hydroxybutyl acrylate (all isomers), N,N-dimethylaminoethyl acrylate, N,N-diethylaminoethyl acrylate, triethyleneglycol acrylate, methacrylamide, N-methylacrylamide, N,N-dimethylacrylamide, N-tert-butylmethacrylamide, N-n-butylmethacrylamide, N-methylolmethacrylamide, N-ethylolmethacrylamide, N-tert-butylacrylamide, N-n-butylacrylamide, N-methylolacrylamide, N-ethylolacrylamide, vinyl benzoic acid (all isomers), diethylaminostyrene (all isomers), alpha-methylvinyl benzoic acid (all isomers), diethylamino alpha-methylstyrene (all isomers), p-vinylbenzene sulfonic acid, p-vinylbenzene sulfonic sodium salt, trimethoxysilylpropyl methacrylate, triethoxysilylpropyl methacrylate, tributoxysilylpropyl methacrylate, dimethoxymethylsilylpropyl methacrylate, diethoxymethylsilylpropylmethacrylate, dibutoxymethylsilylpropyl methacrylate, diisopropoxymethylsilylpropyl methacrylate, dimethoxysilylpropyl methacrylate, diethoxysilylpropyl methacrylate, dibutoxysilylpropyl methacrylate, diisopropoxysilylpropyl methacrylate, trimethoxysilylpropyl acrylate, triethoxysilylpropyl acrylate, tributoxysilylpropyl acrylate, dimethoxymethylsilylpropyl acrylate, diethoxymethylsilylpropyl acrylate, dibutoxymethylsilylpropyl acrylate, diisopropoxymethylsilylpropyl acrylate, dimethoxysilylpropyl acrylate, diethoxysilylpropyl acrylate, dibutoxysilylpropyl acrylate, diisopropoxysilylpropyl acrylate, vinyl acetate, vinyl butyrate, vinyl benzoate, vinyl chloride, vinyl fluoride, vinyl bromide, maleic anhydride, N-phenylmaleimide, N-butylmaleimide, N-vinylpyrrolidone, N-vinylcarbazole, butadiene, isoprene, chloroprene, ethylene and propylene.
Other suitable monomers include cyclopolymerizable monomers such as those disclosed in International Patent Application PCT/AU94/00433 or Moad and Solomon xe2x80x9cThe Chemistry of Free Radical Polymerizationxe2x80x9d, Pergamon, London, 1995, pp 162-171 and ring opening monomers such as those described in Moad and Solomon xe2x80x9cThe Chemistry of Free Radical Polymerizationxe2x80x9d, Pergamon, London, 1995, pages 171-186.
The polymer resulting from the process of the present invention is of the following formula 32: 
where n is a positive integer in the range of from 1 to 100,000, preferably in the range of from 5 to 10000 and more preferably in the range of from 10 to 1000. Qxe2x80x3 in the formula 32 and the formulas below is a repeat unit derived from a monomer selected the goup consisting of maleic anhydride, N-alkylmaleimide, N-arylmaleimide, dialkyl fumarte, cyclopolymerizable monomer, a ring opening monomer, a macromonomer, a vinyl monomer of formula 31(when Qxe2x80x3 will have structure 33) 
and a combination thereof;
wherein L is selected from the group consisting of hydrogen, halogen, and substituted or unsubstituted C1-C4 alkyl, said alkyl substituents being independently selected from the group consisting of OH, ORxe2x80x3, CO2H, CO2CRxe2x80x3, CO2Rxe2x80x3 and a combination thereof;
wherein M is selected from the group consisting of hydrogen, Rxe2x80x3, CO2H, CO2Rxe2x80x3, CORxe2x80x3, CN, CONH2, CONHRxe2x80x3, CONRxe2x80x32, O2CRxe2x80x3, ORxe2x80x3, and halogen; and
Rxe2x80x3 is as defined above.
A in the formula 32 is of the formula 34 below, when D is D1 and E is Zxe2x80x2: 
Thus, when p=1 the resulting polymer will comprise a mixture of the isomers shown in formula 35 below: 
Alternatively, A is of the formula 36 below when D is D2 and E is E1: 
Thus, when p=1, the resulting polymer is of the formula 37 below: 
In yet another embodiment, A is of the formula 38 below when D is D2 and E is E2: 
Thus, when p=1, the resulting polymer is of the formula 39 below: 
Another type of polymer resulting from the process of invention has the following formula 40 (the product will be a mixture of isomers). 
where n is a positive integer in the range of from 1 to 100,000, and D is D3 and E is Z, E1 or E2.
Still other types of polymer resulting from the process of invention has the formula 41 or 41a: 
where n is a positive integer in the range of from 1 to 100,000, and D is D4 and E is E3. 
where n is a positive integer in the range of from 1 to 100,000, and D is D4 and E is E4.
In the context of the present invention, low polydispersity polymers are those with polydispersities that are significantly less than those produced by conventional free radical polymerization. In conventional free radical polymerization, polydispersities of the polymers formed are typically in the range 1.5 to 2.0 at low monomer conversions in the range of from 0.1% to 10% and are substantially greater in the range of from 2 to 10 at higher monomer conversions in the range of from 10% to 100%. Polymers having low polydispersity in the range of from 1.05 to 1.5 are preferred. Those having the polydispersity in the range of 1.05 to 1.3 are more preferred. Moreover, one of the significant advantages of the process of the present invention is that the foregoing low polydispersity can be maintained even at high monomer conversions of in the range of from 10% to 100%.
However, it should be understood, it is also possible, if desired, to produce polymers with broad, yet controlled, polydispersity or multimodal molecular weight distribution by controlled addition of the CTA over the course of the polymerization process of the present invention.
The invention can be used to narrow the polydispersity of polymers formed in polymerizations that would otherwise produce polymers of broad or very broad polydispersities. In this circumstance a preferred polydispersity is one which is less than that formed in the absence of the CTA.
While not wishing to be limited to any particular mechanism, it is believed that the mechanism of the process is as summarized in Scheme 1 below. Propagating radicals Pnxe2x80xa2 are produced by radical polymerization. These can react reversibly with the chain transfer agent RA to form an intermediate radical PnA(xe2x80xa2)R which fragments to give a radical Rxe2x80xa2 (which adds monomer to reinitiate polymerization) and a new transfer agent PnA. This new transfer agent PnA has similar characteristics to the original transfer agent RA in that it reacts with another propagating radical Pmxe2x80xa2 to form an intermediate radical PnA(xe2x80xa2)Pm which fragments to regenerate Pnxe2x80xa2 and form a new transfer agent PmA which has similar characteristics to RA. This process provides a mechanism for chain equilibration and accounts for the polymerization having living characteristics. 
The molecular weight and the polydispersity of the polymer made by the process of the present invention are controlled by one or more of the following:
The polymerization conditions are selected to minimize the number of chains formed from initiator-derived radicals to an extent consistent with obtaining an acceptable rate of polymerization. Termination of polymerization by radical-radical reaction will lead to chains which contain no active group and therefore cannot be reactivated. The rate of radical-radical termination is proportional to the square of the radical concentration. Furthermore, in the synthesis of block, star or branched polymers, chains formed from initiator derived radicals will constitute a linear homopolymer impurity in the final product. These reaction conditions therefore require careful choice of the initiator concentration and, where appropriate, the rate of the initiator feed.
It is also desirable to choose other components of the polymerization medium (for example, the solvents, surfactants, additives, and initiator) such that they have a low transfer constant towards the propagating radical. Chain transfer to these species will lead to the formation of chains which do not contain the active group.
As a general guide in choosing conditions for the polymerization of narrow polydispersity polymers, the concentration of initiator(s) and other reaction conditions [solvent(s) if any, reaction temperature, reaction pressure, surfactants if any, other additives] should be chosen such that the molecular weight of polymer formed in the absence of the CTA is at least twice that formed in its presence. In polymerizations whe radical-radical termination is solely by disprportionation, this equates to choosing an initiator concentration such that the total moles of initiating radicals formed during the polymerization is in the range of 0.000001 times to 0.5 times that of the total moles of CTA. More preferably, conditions should be chosen such that the molecular weight of polymer formed in the absence of the CTA is at least 5-fold that formed in its presence ([initiating radicals]/[CTA] less than 0.2).
Thus, by varying the ratio of the total number of moles of the CTA to the total number of moles of the free radical initiator added to a polymerization medium, the polydispersity of the resulting polymer is controlled. Thus, by decreasing the foregoing ratio, a polymer of lower polydispersity is obtained and by increasing the ratio, a polymer of higher polydispersity is obtained.
With these provisos, the polymerization process according to the present invention is performed under the conditions typical of conventional free-radical polymerization. Polymerization employing the CTAs of the present invention is suitably carried out with temperatures during the reaction in the range xe2x88x9220xc2x0 C. to 200xc2x0 C., preferably in the range 40 to 160xc2x0 C.
Unlike, a conventional free radical polymerization process, the molecular weight of the resulting polymer by the process of the present invention generally increases in a predictable and linear fashion, and may be estimated in accordance with the following relationship:       MW    prod    =                              [                      Moles            ⁢                          xe2x80x83                        ⁢            of            ⁢                          xe2x80x83                        ⁢            monomer            ⁢                          xe2x80x83                        ⁢            consumed                    ]                          [                      moles            ⁢                          xe2x80x83                        ⁢            of            ⁢                          xe2x80x83                        ⁢            CTA                    ]                    xc3x97              MW        mon              +          MW      cta      
where MWprod is the number average molecular weight of the isolated polymer, MWmon is the molecular weight of the monomer and MWcta is the molecular weight of the CTA. The foregoing expression applies under reaction conditions where the number of initiator derived chains is less than 10 percent with respect to total chains and when the added CTA is completely reacted. More complex expressions may be derived to enable prediction of the molecular weight in other circumstances.
By way of illustration, consider the data provided in Examples 19 and 20. A close correspondence is seen between molecular weights calculated according to the above equation and those found experimentally.
The process of this invention can be carried out in emulsion, solution or suspension in either a batch, semi-batch, continuous, or feed mode. Otherwise-conventional procedures can be used to produce narrow polydispersity polymers. For lowest polydispersity polymers, the CTA is added before polymerization is commenced. For example, when carried out in batch mode in solution, the reactor is typically charged with CTA and monomer or medium plus monomer. To the mixture is then added the desired amount of initiator and the mixture is heated for a time which is dictated by the desired conversion and molecular weight.
Polymers with broad, yet controlled, polydispersity or with multimodal molecular weight distribution can be produced by controlled addition of the CTA over the course of the polymerization process.
In the case of emulsion or suspension polymerization the polymerization medium will often be predominantly water and the conventional stabilizers, dispersants and other additives can be present.
For solution polymerization, the polymerization medium can be chosen from a wide range of media to suit the monomer(s) being used. For example, aromatic hydrocarbons, such as, petroleum naphtha or xylenes; ketones, such as, methyl amyl ketone, methyl isobutyl ketone, methyl ethyl ketone or acetone; esters, such as, butyl acetate or hexyl acetate; and glycol ether esters, such as, propylene glycol monomethyl ether acetate.
As has already been stated, the use of feed polymerization conditions allows the use of CTAs with lower transfer constants and allows the synthesis of polymers that are not readily achieved using batch polymeization processes. If the polymerization is carried out as a feed system the ration can be carried out as follows. The reactor is charged with the chosen polymerization medium, the CTA and optionally a portion of the monomer mixture. Into a seperate vessel is placed the remaining monomer mixture. The free radical initiator is dissolved or suspended in polymerization medium in another separate vessel. The medium in the reactor is heated and stirred while the monomer mixture+medium and initiator+medium are introduced, for example by a syringe pump or other pumping device. The rate and duration of feed is determined largely by the quantity of solution, the desired monomer/CTA/initiator ratio and the rate of the polymezation. When the feed is complete, heating may be continued for an additional period. Sequential addition of different monomers will give a block or gradient copolymer.
Following completion of the polymerization, the polymer can be isolated by stripping off the medium and unreacted monomer(s) or by precipitation with a non-solvent. Alternatively, the polymer solution/emulsion can be used as such, if appropriate to its application.
The process of the present invention is compatible with a wide variety of monomers and can be used under varied reaction conditions to produce polymers having low polydispersity. By varying the rate of monomer(s) addition or by varying the sequence in which the monomer(s) may be added to the polymerization medium, the process present invention may be used to produce block and multi-block and gradient polymers. By selecting the functionalities desired, an end-functional polymer of specific end functionalities can be readily produced.
Examples of CTAs of the formula 6 which are precursors to graft polymers of formula 32, which include copolymers and/or xanthate or dithiocarbamate derivative of the following formula 42: 
when in the formula 32, p=n and R is of the following formula 43: 
Examples of CTAs containing functionality attached to a common nucleus are described below.
When in the formula 6 p=2, R=p-xylylene, the CTA is of the formula 44 below: 
and when in the formula 10, pxe2x80x2xe2x80x3=2, E=E4, Gxe2x80x2xe2x80x3=p-phenylene then the CTA is of the formula 45 below: 
The compound of the following formula (46) will provide a star polymer, as shown below: 
When in the formula 6, p=4 and R is of the following formula 47 below: 
The polydispersity obtained under a given set of reaction conditions is sensitive to the value of the transfer constant (Ctr). Lower polydispersities will result from the use of CTAs with higher transfer constants. According to the above mechanism, the chain transfer activities of the reagents (RA, PnA and PmA) will be determined by the reactivity of the Cxe2x95x90S double bond and by the rate of fragmentation and the partitioning of the intermediate radicals between starting materials and products.
Mxc3xcller et al. have derived relationships which enable polydispersites to be estimated for polymerizations which involve chain equilibration by reversible chain transfer (Mxc3xcller, A. H. E.; Zhuang. R.; Yan, D.; Litvenko, G. Macromolecules, 28, 4326 (1995))
Mw/Mn=1+1/Ctr
Where Ctr is the chain transfer constant.
This above relationship should apply to batch polymerizations carried to full conversion in the situation where the number of initiator-radical derived chains is small with respect to total chains and there are no side reactions. This relationship suggests that the transfer constant should be greater than 2 to obtain a polydispersity  less than 1.5 in a batch polymerization.
For a feed polymerization in which the monomer concentration is kept constant by continual replenishment, Mxc3xcller et al. suggest that the following relationship should hold (Mxc3xcller, A. H. E.; Litvenko, G., Macromolecules 30, 1253 (1997)):
Mw/Mn=1+(2/DPn)(1/Ctr)([M]/[CTA])
Where Ctr is the chain transfer constant and DPn is the degree of polymerization of the product.
A possible mechanism of the addition-fragmentation step, without reliance thereon, for the case of compounds of the formula 2 where D is D1 is as follows: 
The foregoing proposed mechanism is in accord with experimental observations. According to this mechanism, the X group may in principle be any group which maintains conjugation between the Cxe2x95x90S and the Sxe2x80x94R groups. Some possible structures are included in the following formulas 48-50: 
Other examples of CTAs with conjugating groups are of the following formulas 51-53 below: 
Structures containing multiple alkylthio groups allow the synthesis of polymers of more complex architecture. For example the following compound can give rise to a three arm star 54 as follows: 
Sequential addition of monomers will give rise to block copolymers.
It will be clear to those skilled in the art that to be effective as a CTA in the present invention, the group R of the CTA must be both a free radical leaving group and a species that initiates free radical polymerization. Leaving group ability is determined both by steric factors and by radical stability. Examples of preferred R groups for the CTA are benzyl derivatives (xe2x80x94CRxe2x80x2xe2x80x32Ph) and cyanoalkyl derivatives (xe2x80x94CRxe2x80x2xe2x80x32CN) and other moieties known to the art as free radical leaving groups.
The leaving group ability of Rxe2x80xa2 will also be determined by the nature of the propagating species formed in the polymerization. For example, in styrene polymerization, R is preferably selected from the group consisting of benzyl, 1-phenylethyl, 2-phenylpropyl, 2-(alkoxycarbonyl)prop-2-yl, 2-cyanoprop-2-yl, 2-cyanobut-2-yl, and 1-cyanocyclohexyl. In methyl methacrylate polymerization R is preferrably selected from the group consisting of 2-phenylpropyl, 2-cyanoprop-2-yl, 2-cyanobut-2-yl, and 1-cyanocyclohexyl. In vinyl acetate polymerization R is preferably selected from the group consisting of 2-(alkoxycarbonyl)prop-2-yl, cyanomethyl, 2-cyanoprop-2-yl, 2-cyanobut-2-yl, and 1-cyanocyclohexyl.
To avoid retaration the Rxe2x80x2xe2x80x3, substituents should be chosen such that Rxe2x80xa2 gives facile addition to the monomer. In this context, the preferred Rxe2x80x2xe2x80x3 groups are independently selected from the group consisting of hydrogen and substituted alkyl. The ability of Rxe2x80xa2 to initiate polymerization will be determined by the nature of the monomers used in the polymerization. In polymerization of styrene and methacrylates benzyl derivatives (xe2x80x94CRxe2x80x2xe2x80x32Ph) and cyanoalkyl derivatives (xe2x80x94CRxe2x80x2xe2x80x32CN) are effective. However, in vinyl acetate polymerization benzyl derivatives (xe2x80x94CRxe2x80x2xe2x80x32Ph) are slow to initiate polymerization, and retardation may be observed, but cyanoalkyl derivatives (xe2x80x94CRxe2x80x2xe2x80x32CN) and the corresponding esters (xe2x80x94CRxe2x80x2xe2x80x32CO2Alkyl) are effective.
In polymerizations of (meth)acrylates and styrene, we have discovered that dithiocarbamate CTAs (formula 2, D=D2, E=E1) with conjugating or electron withdrawing substituents at the dithiocarbamate nitrogen are substantially more effective than dithiocarbamate derivatives with simple alkyl substituents.
Thus, the preferred groups in E1 for this application are aromatic nitrogen heterocycles where G-N-J forms part of aromatic cyclic group, such as those of the following formulas 55 and 56 below: 
and groups in E1 such as cyclic amides where G-N-J forms part of a non-aromatic cyclic group with substituent such as oxo conjugated to nitrogen as in the following formulas 57-59 below: 
One possible explanation for the greater activity of the above dithiocarbomate is in terms of a higher reactivity of the Cxe2x95x90S double bond towards free radical addition. This is attributed to the effect of the conjugating or electron withdrawing substituents giving greater double bond character to the Cxe2x95x90S double bond.
In carbamates and amides the Nxe2x80x94CO link has partial double bond character as a result of the delocalisation of the non-bonded nitrogen lone pair with the p electrons of carbonyl group (Deslongchamps, P. Stereoelectronic effects in organic chemistry, Pergamon Press, NY, 1983). As a result, the oxygen of the carbonyl group has a partial negative charge. Since sulfur has a higher electron affinity than oxygen, this effect would be expected to be more pronounced in dithiocarbamates. 
If the nitrogen lone pair participates in an alternate xcfx80-system (e.g. the aromatic pyrrole ring) the lone pair will be less available for delocalization into the thiocarbonyl bond resulting in a greater double bond character for the Cxe2x95x90S double bond and hence a greater reactivity of the CTA towards radicals.
Similar considerations apply in the case of xanthate esters. We have found that effectiveness of xanthate ester CTAs (formula 2, D=D2, E=E2) in providing low polydispersity polymers in acrylate polymerization increases in the series where Gxe2x80x2 is xe2x80x94OEt less than xe2x80x94OC6H5 less than C6F5.
The transfer constants of dithiocarbamate and xanthate derivatives (compounds of formula 2 D=D2, E=E1 or E2 repectively) are strongly dependent on the monomer used. Thus dithiocarbamate and xanthate derivatives of formula 2 with D=D2 and E=E1 or E2 wherein G, J, and Gxe2x80x2 are independently selected from the group consisting of substituted or unsubstituted alkyl, substituted or unsubstituted alkylene, substituted or unsubstituted aryl, substituted or unsubstituted heterocyclyl have relatively low transfer constants in polymerization of methacrylate or styrene monomers and are not effective in giving narrow polydispersity polymers in batch polymerization of such monomers.
However in polymerization of vinyl acetate, vinyl butyrate, vinyl benzoate, vinyl chloride, vinyl bromide, vinyl fluoride, N-vinylpyrolidone, N-vinylcarbazole and similar vinyl monomers these dithiocarbamate and xanthate derivatives (compounds of formula 2, D=D2, E=E1 or E2) have higher transfer constants enabling low polydispersity polymers to be achieved. Preferred CTAs for use with these vinyl monomers include compounds of formula 2 with D=D2 and E=E1 or E2 wherein G, J, and Gxe2x80x2 are independently selected from the group consisting of substituted or unsubstituted alkyl, substituted or unsubstituted alkylene, substituted or unsubstituted aryl, substituted or unsubstituted heterocyclyl, or when E=E1, G-N-J forms part of a non-aromatic cyclic group.
The invention has wide applicability in the field of free radical polymerization and can be used to produce polymers that are suitable for use in compositions for coatings, including automotive OEM and refinishes, as primers, basecoats, undercoats, overcoats and clear coats. The polymers are also suitable for use in compositions for maintenance finishes for a wide variety of substrates, such as steel, copper, brass and aluminum or non-metallic substrates, such as, wood, leather and concrete.
A coating composition containing the polymer prepared by the process of the present invention may also contain conventional additives, such as, pigments, stabilizers, flow agents, toughening agents, fillers, durability agents, corrosion and oxidation inhibitors, rheology control agents, metallic flakes and other additives. Such additional additives will, of course, depend on the intended use of the coating composition. Fillers, pigments, and other additives that would adversely effect the clarity of the cured coating will not be included if the composition is intended as a clear coating.
Block and star, and branched polymers can be used as compatibilizers, thermoplastic elastomers, dispersing agents, flocculants, surfactants, rheology control agents or as additives to modify the surface properties of bulk polymers and plastics. Additional applications for polymers of the invention are in the fields of imaging, electronics (e.g., photoresists), engineering plastics, adhesives, sealants, paper coatings, printing inks, and polymers in general.
The invention can also be applied to the controlled grafting of polymer chains onto solid polymers or surfaces for the purpose of controlling biocompatibility, biostability, hydrophilicity, hydrophobicity, adhesion or friction.